This invention relates to thermal protective systems, structures and methods for protecting underlying substrates such as structural beams and columns, tanks, electrical cables and cable trays, junction boxes and other containers, and various other substrates which may be subjected to thermal extremes and flame.
Numerous thermal protective coating materials and systems for applying them are known. Some of the materials are foamed passive insulative materials which protect merely by their low thermal conductivity and their thickness as applied. These include foamed cement or intumesced silicates. Other materials provide active thermal protection. Some intumesce when heated to form a thick closed cell protective layer over the substrate. These include silicate solutions or ammonium phosphate paints or materials such as those disclosed in Nielsen et al., U.S. Pat. No. 2,680,077 or Kaplan, U.S. Pat. No. 3,284,216. Other active thermal protective materials include constituents which sublime at a predetermined temperature, such as those disclosed in Feldman, U.S. Pat. No. 3,022,190. The active thermal protective materials disclosed in Feldman, U.S. Pat. No. 3,849,178 are particularly effective; when subjected to thermal extremes, these materials both undergo an endothermic phase change and expand to form a continuous porosity matrix.
Various methods and structures have also been used or proposed for applying these thermal protective coating materials. The most frequent approach is to apply the materials directly to the substrate, without additional structure. For many applications, however, a reinforcing material, such as fiberglass sheet or a wire mesh, has been embedded in the coating material to strengthen the material and prevent it from cracking or falling off the substrate under conditions of flame or thermal extreme. Examples of this approach are found in Feldman, U.S. Pat. Nos. 3,022,190, Billing et al, 3,913,290, Kaplan, 3,915,777, and Billing et al, 4,069,075. Sometimes the materials are first applied to a reinforcing structure such as a flexible tape or flexible wire mesh, and the combined structure is applied to the substrate. Examples of this approach are found in Feldman, U.S. Pat. Nos. 3,022,190, Pedlow, 4,018,962, Peterson et al, 4,064,359, Castle, 4,276,332, and Fryer et al, 4,292,358. In these last-mentioned systems, the purpose of the reinforcing structure may be both to strengthen the resulting composite and to permit its application to a substrate without directly spraying, troweling or painting the uncured coating materials onto the substrate. In any of the foregoing methods and structures, multiple layers are frequently applied to the substrate to provide additional protection.
All of the presently known materials, structures and methods suffer from certain defects. For example, they provide less protection than desirable from prolonged and extreme thermal conditions. Even the active compositions add substantial weight to the substrate. Many of the more effective systems are difficult and expensive to install. They are also subject to loss of effectiveness or failure after being applied, for example if they are subjected to severe vibration.